1. Field of the Invention
The invention relates to automatic low pressure tire indicator assemblies and, more particularly, but not by way of limitation, it relates to an improved method and apparatus for sensing and indicating low tire pressure.
2. Description of the Prior Art
The prior art includes a great number of indicating devices that warn of pressure drop in pneumatic tires, and such tire aids have developed over a long number of years. A U.S. Pat. No. 4,819,686 teaches a valve cap adaptation which shows visually any appreciable tire pressure drop by using a deflectable diaphragm that moves in response to a reference air pressure toward a compartment having existing tire pressure, and the moving diaphragm provides a visual indication within a transparent housing portion of the valve cap. A U.S. Pat. No. 2,866,432 also teaches a movable diaphragm type of indicator which may be detachably secured to a valve stem for subsequent actuation manually to indicate by sound, sight or touch whether or not the pressure within the tire is equal to or above the required amount.
A U.S. Pat. No. 4,244,214 is of interest in that it describes a device that includes an axially appertured bolt that is movably mounted within a visual tire valve with respect to an indicating window. The bolt includes a series of different color bands which show a gradation in tire pressure. Also, U.S. Pat. No. 3,990,467 is of interest for its capability of indicating tire air pressure by color whenever the tire is under or over inflated. Finally, a U.S. Pat. No. 3,830,249 is cited for its ability to give audible indication of over pressure situations; that is, when the tire receives additional inflation pressure, it makes an audible sound while surplus air is being discharged down to a recommended pressure level.